Recently, use of audio data representing sound such as music and the like by distributing it via a network such as the Internet and the like, and recording it on a recording medium such as a mini disk (MD) has been actively pursued. As such, with audio data which is distributed across networks or recorded on a recording medium, increase in data amount and widening of the occupation band width due to the excessively widened band width needs to be avoided. Therefore, normally, components of a specified frequency or greater are removed from the music and the like to be supplied.
For example, components of approximately 16 kHz or greater are removed from MP3 (MPEG1 audio layer 3) format audio data and ATRAC 3 (Adaptive TRansform Acoustic Coding 3) format audio data.
High-frequency components of approximately 16 kHz or greater are removed as such because components of frequencies exceeding the audible region are considered unnecessary in relation to human hearing capacity. However, it has been pointed out recently that signals completely removed of high-frequency components may have slightly changed tone quality, which may be deteriorated from that of the original music.
Therefore, many devices for high-frequency component interpolation have been made conventionally. For example, an apparatus which generates an interpolation signal by converting the frequency of a to-be-interpolated signal, as disclosed in Japanese Unexamined Patent Application Publication No. 2004-184472 (hereafter abbreviated as Patent Document 1), and an apparatus which generates an interpolation signal without correlation to the original signal and adds it to a high-frequency signal, as disclosed in Japanese Unexamined Patent Application Publication No. Hei 2-311006 (hereafter abbreviated as Patent Document 2) are well-known. The technology disclosed in Patent Document 2 extracts the high-frequency component of a white noise signal, which is generated by a white noise generator and does not have correlation with the original signal, and adds it to the original signal.